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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

The Corrosion Behavior of Zn/Graphene Oxide Composite Coatings Fabricated by Direct Current Electrodeposition

The zinc (Zn) and Zn/graphene oxide (Zn/GO) composite coatings on the mild steel were fabricated by direct current electrodeposition from an acidic chloride bath without GO and that with four different concentrations (50, 100, 200 and 300 mg/L) of GO, respectively. The GO first is synthesized by using the typical Hummer method. Physical characterizations including the surface and cross-sectional morphology, chemical composition and crystal structure of the Zn and Zn/GO composite coatings were done by scanning electron microscope, energy-dispersive x-ray and x-ray diffraction. The crystalline size, texture coefficient, water contact angle and hardness of the Zn and Zn/GO composite coatings were measured. The corrosion behavior of the Zn and Zn/GO composite coatings was studied by the electrochemical corrosion tests including the potentiodynamic polarization test and the electrochemical impedance spectroscopy test and the immersion test. The result reveals that the corrosion resistance of the Zn coating is remarkably increased by the incorporation of GO. Furthermore, it does not show a linear increase with the increase in the amount of incorporated GO and an optimal corrosion resistance is provided by the Zn/GO composite coating attained from the electrolyte containing 100 mg/L GO. The influence of the incorporation of GO on the corrosion resistance of the Zn coating is explained in combination with their physical characterizations.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS1990

The theory of an auto-resonant field emission cathode relativistic electron accelerator for high efficiency microwave to direct current power conversion

A novel method of microwave power conversion to direct current is discussed that relies on a modification of well known resonant linear relativistic electron accelerator techniques. An analysis is presented that shows how, by establishing a 'slow' electromagnetic field in a waveguide, electrons liberated from an array of field emission cathodes, are resonantly accelerated to several times their rest energy, thus establishing an electric current over a large potential difference. Such an approach is not limited to the relatively low frequencies that characterize the operation of rectennas, and can, with appropriate waveguide and slow wave structure design, be employed in the 300 to 600 GHz range where much smaller transmitting and receiving antennas are needed.

Manning, Robert M.↗
DOE OSTI2024

Navigating the Use of Direct Current in Residential Settings: Merits and Obstacles

This review paper provides an in-depth analysis of the role of Direct Current (DC) power systems in residential settings, focusing on their safety, efficiency, and environmental advantages. It recognizes the significant contribution of the residential sector to global carbon dioxide emissions and explores how DC power systems can help mitigate these effects. The paper traces the historical evolution of DC power, its resurgence with renewable energy technologies, and the advancements in power electronics that facilitate its integration. Emphasizing the efficiency and safety benefits, especially in low-voltage applications, the paper highlights the seamless integration of DC systems with inherently DC-generating renewable sources like solar PV and wind. The review discusses the critical role of converter technologies in the transition to DC power and examines the compatibility of DC systems with energy storage solutions, underscoring their potential for enhanced energy management. It also addresses the environmental impacts of adopting DC power, aligning with global carbon reduction efforts. The paper analyzes regional case studies, exploring practical applications and outcomes, and addresses challenges such as the need for standardization. It concludes with recommendations for stakeholders and future research directions, emphasizing the economic, technological, and environmental aspects of DC power systems. Overall, the paper presents DC power as a viable and sustainable option for residential energy conservation, contingent upon ongoing technological progress, supportive policies, and standardization.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2016

A superconducting direct-current limiter with a power of up to 8 MVA

A resistive switching superconducting fault current limiter (SFCL) for DC networks with a nominal voltage of 3.5 kV and a nominal current of 2 kA was developed, produced, and tested. The SFCL has two main units—an assembly of superconducting modules and a high-speed vacuum circuit breaker. The assembly of superconducting modules consists of nine (3 × 3) parallel–series connected modules. Each module contains four parallel-connected 2G high-temperature superconducting (HTS) tapes. The results of SFCL tests in the short-circuit emulation mode with a maximum current rise rate of 1300 A/ms are presented. The SFCL is capable of limiting the current at a level of 7 kA and break it 8 ms after the current-limiting mode begins. The average temperature of HTS tapes during the current-limiting mode increases to 210 K. After the current is interrupted, the superconductivity recovery time does not exceed 1 s.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

A Scalable Test-Bed for Direct Current Current Transformer Automated Functional Testing and Characterization

This article describes a scalable test-bed for automation of measurements of the direct current current transformers (DCCT). Automation of measurement involves functional measurements, fault event based measurements and data validation. The test-bed is designed to measure up to 20 DCCTs at a time with software based measurement repetition checks and validation of the measurements.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Method and system for a gas tube switch-based voltage source high voltage direct current transmission system

A voltage source converter based high-voltage direct-current (HVDC) transmission system includes a voltage source converter (VSC)-based power converter channel. The VSC-based power converter channel includes an AC-DC converter and a DC-AC inverter electrically coupled to the AC-DC converter. The AC-DC converter and a DC-AC inverter include at least one gas tube switching device coupled in electrical anti-parallel with a respective gas tube diode. The VSC-based power converter channel includes a commutating circuit communicatively coupled to one or more of the at least one gas tube switching devices. The commutating circuit is configured to "switch on" a respective one of the one or more gas tube switching devices during a first portion of an operational cycle and "switch off" the respective one of the one or more gas tube switching devices during a second portion of the operational cycle.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2016

Statistical characteristic in time-domain of direct current corona-generated audible noise from conductor in corona cage

The corona-generated audible noise (AN) has become one of decisive factors in the design of high voltage direct current (HVDC) transmission lines. The AN from transmission lines can be attributed to sound pressure pulses which are generated by the multiple corona sources formed on the conductor, i.e., transmission lines. In this paper, a detailed time-domain characteristics of the sound pressure pulses, which are generated by the DC corona discharges formed over the surfaces of a stranded conductors, are investigated systematically in a laboratory settings using a corona cage structure. The amplitude of sound pressure pulse and its time intervals are extracted by observing a direct correlation between corona current pulses and corona-generated sound pressure pulses. Based on the statistical characteristics, a stochastic model is presented for simulating the sound pressure pulses due to DC corona discharges occurring on conductors. The proposed stochastic model is validated by comparing the calculated and measured A-weighted sound pressure level (SPL). The proposed model is then used to analyze the influence of the pulse amplitudes and pulse rate on the SPL. Furthermore, a mathematical relationship is found between the SPL and conductor diameter, electric field, and radial distance.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Structure, mechanical, and frictional properties of hydrogenated fullerene-like amorphous carbon film prepared by direct current plasma enhanced chemical vapor deposition

In this study, fullerene like carbon (FL-C) is introduced in hydrogenated amorphous carbon (a-C:H) film by employing a direct current plasma enhanced chemical vapor deposition. The film has a low friction and wear, such as 0.011 and 2.3 × 10{sup −9}mm{sup 3}/N m in the N{sub 2}, and 0.014 and 8.4 × 10{sup −8}mm{sup 3}/N m in the humid air, and high hardness and elasticity (25.8 GPa and 83.1%), to make further engineering applications in practice. It has several nanometers ordered domains consisting of less frequently cross-linked graphitic sheet stacks. We provide new evidences for understanding the reported Raman fit model involving four vibrational frequencies from five, six, and seven C-atom rings of FL-C structures, and discuss the structure evolution before or after friction according to the change in the 1200 cm{sup −1} Raman band intensity caused by five- and seven-carbon rings. Friction inevitably facilitates the transformation of carbon into FL-C nanostructures, namely, the ultra low friction comes from both such structures within the carbon film and the sliding induced at friction interface.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Synthesis of Highly Oriented Zinc-Oxide Films on Amorphous Substrates by the Method of Direct-Current Magnetron Sputtering

We describe the technology of obtaining highly oriented zinc-oxide (ZnO) films on amorphous substrates at high growth rates (up to 7 nm/s) by means of direct-current magnetron sputtering. It is suggested to optimize the substrate position with respect to magnetron and consider the floating potential to which the substrate is charged in magnetron discharge plasma as one of the main technological parameters. Electrondiffraction study of the structural characteristics of the obtained ZnO films showed that increase in the substrate temperature was accompanied by transformation of the crystallite shape from platelike to columnar.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Technologies for providing secure emergency power control of high voltage direct current transmission system

Technologies for providing secure emergency power control of a high voltage direct current transmission (HVDC) system include a controller. The controller includes circuitry configured to receive status data indicative of a present physical status of a power system. The circuitry is also configured to obtain an emergency power control command triggered by a remote source. The emergency power control command is to be executed by an HVDC transmission system of the power system. Further, the circuitry is configured to determine, as a function of the status data, whether the emergency power control command is consistent with the present physical status of the power system and block, in response to a determination that the emergency power control command is not consistent with the present physical status of the power system, execution of the emergency power control command by the HVDC transmission system.

Pan, Jiuping↗
DOE OSTI2024

Coherent High-Frequency Axial Oscillations in a Partially Magnetized Direct Current Magnetron Discharge

High-frequency oscillations are observed in a neon plasma of a direct current magnetron discharge. At low discharge currents, we see highly coherent 60 MHz fluctuations. Above a distinct current threshold, secondary 5–10 MHz fluctuations emerge in addition to turbulent fluctuations in the 60–100 MHz range. The oscillations in the total discharge current suggest axial wave propagation. A lower-hybrid wave theory is invoked to model the high-frequency oscillations. Here, we attribute the low-frequency modes to a turbulence-driven inverse cascade process, as suggested by recent simulations.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2025

Advancing Temperature Monitoring of the Bottom Anode in a Direct Current Electric Arc Furnace Operations with Distributed Optical Fiber Sensors.

The bottom anode in the Direct Current Electric Arc Furnace (DC EAF) is critical for completing the electrical circuit necessary for sustaining the arc within the furnace. For pin-type bottom anodes, monitoring of the temperature of select pins instrumented with thermocouples is performed to track bottom wear in the EAF and inform the operator when the furnace should be removed from service. Furthermore, this work presents the results from a plant trial using distributed temperature monitoring of bottom anode pins in a 165-ton DC EAF over a two-month service period utilizing two optical fiber sensing techniques: fiber Bragg grating (FBG) and Rayleigh backscattering (RBS). The early detection of temperature anomalies along the length of the anode pin through distributed sensing enhances operational safety, providing a robust alternative to traditional thermocouples.

42 ENGINEERING↗
DOE OSTI2016

Control of plasma properties in a short direct-current glow discharge with active boundaries

To demonstrate controlling electron/metastable density ratio and electron temperature by applying negative voltages to the active (conducting) discharge wall in a low-pressure plasma with nonlocal electron energy distribution function, modeling has been performed in a short (lacking the positive-column region) direct-current glow discharge with a cold cathode. The applied negative voltage can modify the trapping of the low-energy part of the energetic electrons that are emitted from the cathode sheath and that arise from the atomic and molecular processes in the plasma within the device volume. These electrons are responsible for heating the slow, thermal electrons, while production of slow electrons (ions) and metastable atoms is mostly due to the energetic electrons with higher energies. Increasing electron temperature results in increasing decay rate of slow, thermal electrons (ions), while decay rate of metastable atoms and production rates of slow electrons (ions) and metastable atoms practically are unchanged. The result is in the variation of electron/metastable density ratio and electron temperature with the variation of the wall negative voltage.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

High sensitivity measurement system for the direct-current, capacitance-voltage, and gate-drain low frequency noise characterization of field effect transistors

Measurements of current fluctuations originating in electron devices have been largely used to understand the electrical properties of materials and ultimate device performances. In this work, we propose a high-sensitivity measurement setup topology suitable for the automatic and programmable Direct-Current (DC), Capacitance-Voltage (CV), and gate-drain low frequency noise characterization of field effect transistors at wafer level. Automatic and programmable operation is particularly useful when the device characteristics relax or degrade with time due to optical, bias, or temperature stress. The noise sensitivity of the proposed topology is in the order of fA/Hz{sup 1/2}, while DC performances are limited only by the source and measurement units used to bias the device under test. DC, CV, and NOISE measurements, down to 1 pA of DC gate and drain bias currents, in organic thin film transistors are reported to demonstrate system operation and performances.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2023

Reliability of Open Public Electric Vehicle Direct Current Fast Chargers

The aim was to systematically evaluate the usability of all public electric vehicles (EV) direct current fast chargers (DCFC) in the San Francisco region. To achieve a rapid transition to EVs, a highly reliable and easy to use charging infrastructure is critical to building confidence among consumers. The functionality and usability of all 182 open, public DCFC charging stations with CCS connectors (combined charging system) in the 9 counties of the Bay Area were tested (655 electric vehicle service equipment (EVSE) ports). An EVSE was classified as functional if it charged an EV for 2 minutes. Overall, 73.3% of the 655 EVSEs were functional. The causes of the nonfunctioning EVSEs (23.5%) were blank or unresponsive screens or error messages; payment system failures; charge initiation failures; network failures; or broken connectors. In addition, the cable was too short to reach the EV inlet for 3.2% of the EVSEs. A random sampling of 10% of the EVSEs, approximately 8 days after the first evaluation, found no overall change in functionality. The level of functionality found with field testing conflicts with the 95–98% uptime reported by the EV service providers (EVSPs) who operate the EV charging stations. There is a need for precise and verifiable definitions of uptime, downtime, and excluded time, as applied to public EV chargers. In conclusion, the level of failure of the existing public EV DCFC charge infrastructure highlights the importance of improving the system design and maintenance to improve adoption of EVs.

33 ADVANCED PROPULSION SYSTEMS↗